Function notation is the official way to write a function. The previous example f(x) = 2x+1 is an example of function notation. The f(x) part is read "f of x", and it names the function f. It also identifies the input variable, which in this case is x.
WARNING: As the lyrics to the song explain, the f(x) does NOT mean f times x. Most people see the parenthesis and assume it means multiplication, but this is not true.
Example 1: Translate g(y) = -5y - 9 into words.
Answer: g of y equals negative five y minus nine.
Take 3 minutes to check out this website. Stop reading once you get to the examples.